IMMUNITY. 25 



does not dialyze ; it is precipitated by alcohol, and preserves 

 its activity, to a considerable extent, after precipitation. It is 

 soluble in glycerin, and is said to have the general characters 

 of a " globulin." The experimenters named also succeeded in 

 conferring immunity upon susceptible animals by injecting into 

 them blood-serum containing this antitoxin. According to the 

 Italian investigators named, the antitoxins of tetanus and of 

 rabies are found only in the blood-serum of immune animals, 

 and not in the tissues (nervous or muscular), or in the paren- 

 chyma of the various organs. 



Professor Ehrlich, of Berlin, in 1891, published the results of 

 some researches which have an important bearing upon the 

 explanation of acquired immunity, and which show that suscepti- 

 ble animals may be made immune against the action of certain 

 toxic proteids of vegetable origin, other than those produced 

 by bacteria ; also that this immunity depends upon the pres- 

 ence of an antitoxin in the blood-serum of the immune animals. 



In a later paper (1892) Ehrlich has given an account of 

 subsequent experiments which show that the young of mice, 

 which have an acquired immunity for these vegetable toxal- 

 bumins, may acquire immunity from the ingestion of their 

 mother's milk ; and also that immunity from tetanus may be 

 acquired in a brief time by young mice through their mother's 

 milk. In his tetanus experiments Ehrlich used blood-serum 

 from an immune horse to give immunity to the mother-mouse 

 when her young were already seventeen days old. Of this 

 blood-serum 2 c.c. was injected at a time on two successive 

 days. The day after the injection one of the sucklings received 

 a tetanus inoculation, by means of a splinter of wood to which 

 spores were attached. The animal remained in good health, 

 while a much larger control mouse, inoculated in the same way, 

 died of tetanus at the end of twenty-six hours. Other suck- 

 lings, inoculated at the end of forty-eight hours and of seventy- 

 two hours after the mother had received the injection of blood- 

 serum, likewise remained in good health, while the control 

 mice died. 



The possibility of conferring immunity by means of the milk 

 of an immune animal is further shown by the experiments of 



